This study was undertaken to determine the mechanism whereby mutants at the suppressor-of-sable [su(s)] locus are able to suppress specific mutants at other loci in Drosophila melanogaster. Evidence from another Drosophila suppressor system suggests that the suppressible alleles may all be mutants caused by the insertion of a specific mobile genetic element. Our approach to answering this question will involve the molecular cloning of both the su(s) locus and the vermilion (v) locus, several alleles of which are suppressible. We will determine the product of su(s) and how it interacts at the molecular level with the suppressible vermilion alleles to effect suppression.